Light curtain blockage time.

OK guys I have an application that will be a retrofit. I DID NOT DESIGN THE FIRST SYSTEM. This is a loading system. The operator unloads a barrel from a truck to a machine.
This is in a class 1 div 2 area. The current light curtain-ish type of configuration is a row of retro-reflective photoeyes. If there is product in the way of the photoeyes the machine will not run. Once the product is no longer in the way a machine can run.

The customer wants a to use a light curtain in a configuration that if the light is blocked the machine will not move. If the light curtain is blocked for an extended amount if time the system will go into a global shutdown.

AB safety processor. I'm thinking of 2 safety functions. 1st function just to stop the machine motion with an automatic reset. The 2nd would be after xx.xx seconds the stop would be global and a manual reset to verify the work cell was clean of people.

The risk assessment states the a presence sensing device should be used and the machine should not run when blocked.

What am I missing? I think I have everything covered.

Is there any chance a person could walk through the light curtain and the machine re-engage once they are past the curtain? That would be my concern with auto-resetting after breaking the light curtain.

This almost sounds like it is an application for an area scanner instead of a light curtain, if at all feasible.

You have to be careful. Who is responsible for the riska assessment ? You are going to interfere with the safety on a machine, so you cannot just say that you are unaware of the safety.

The current light curtain-ish type of configuration is a row of retro-reflective photoeyes.

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If it is for safety of persons they must be safety rated and installed according to documentation.

If there is product in the way of the photoeyes the machine will not run

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That sounds as if the function protects the machine and/or the product, not persons.

The risk assessment states the a presence sensing device should be used and the machine should not run when blocked

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Does it say that it is because a person can be in the way ?
Maybe the risk is that in case of a serious malfunction parts or material can come flying out of the machine. In that case it should be guarded against by covers and shields that are strong enough to contain the parts or the material.

The operator unloads a barrel from a truck to a machine.

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Even if the normal way of operation does not involve that the operator reaches into the machine, then it sounds as if you cannot rule out that he dont need to reach into the machine to clear a malfunction or to adjust a barrel etc.

Again, be careful, it sounds as a very dangerous process, and as far as I know, in the US you can get personally liable.
I can imagine so many risks, in particular because a truck is involved. How is the process safeguarded against one person being hit, getting caught, trapped, crushed etc when another person is using a truck to insert a barrel into the machine ?

You wouldn't get through the opening in under 4 seconds. This is a classified area. I can't find an area scanner rated for classified installations.

JeffKiper said:

You wouldn't get through the opening in under 4 seconds.

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That helps if there is a risk due to the inertia of moving parts when stopping.
But it does not help against anything else.

Even if the machine stops when the light curtain is interrupted, you also have to consider if for example a stuck barrel can tip or fall. So it is not enough to think that just be removing the external energy from the machine, it will then be safe.

I am out on medical today, so don't have my references, but I'm pretty sure a safety function cannot be auto resetting.
I would check into that.

my two cents.

Retrofit or upgrade doesn't matter.
once you modify the current hardware, software, or plc program, you will be assuming all liability of the machine operation from this point on and you must bring it up to current safety requirements.

you are only allowed to blank out so many photo eyes in a light curtain if memory serves me correctly, for example, sheet metal feeding into a punchpress. beyond that, there is a size limitation before the system has to trip.

if this is for a part, you may be ok, but if what you are proposing will allow any part of the human body to go through the light curtain and be in danger, or if you can pass through the light curtain and it not trip, then you cannot do it.

it has been several years since I had to deal with light curtains, but this is what I remember.

james

Dont just focus on the ligh curtain.
If someone gets hurt because of a risk that was in the original machine, and it wasnt safeguarded in the original design, then that is not an argument for you not being responsible and liable.

This needs to be more of a one way street, you tell the customer what can or cannot be done both legally and safely and how much it will cost.

If they don't have the money, then walk away.

Safety on a budget or on the whim of a customer, designed on a back of a fag packet, is a recipe for disaster.